1. Field of the Invention
The present invention relates to a hydraulic pressure control apparatus for an automatic transmission mounted on a vehicle or the like and more particularly to a hydraulic pressure control apparatus which prevents a lockup clutch from becoming engaged when a solenoid valve fails.
2. Description of the Related Art
Conventionally, in an automatic transmission mounted on a vehicle or the like, particularly an automatic transmission having a continuously variable transmission (CVT), a torque converter is provided between a drive source such as an engine and an input shaft of that automatic transmission. The torque converter contains a lock-up clutch, which is engaged to couple a front cover to which output rotation of the engine is input from the input shaft. Usually, the lock-up clutch is engaged when the vehicle is traveling, so that the rotation of the engine is connected directly to the input shaft of the automatic transmission so as to improve fuel economy.
The aforementioned lockup clutch is controlled by the hydraulic controller of the automatic transmission, whereby it is engaged or released. If any trouble such as a short-circuit occurs in the hydraulic controller (failure), the vehicle may be stopped with the lockup clutch engaged. Because the vehicle wheels are connected directly to the engine by engagement of the lock-up clutch, the engine is stopped immediately when the vehicle stops, i.e., so-called engine stall occurs. If the engine is stopped, the vehicle needs to be towed for repair because the vehicle cannot travel. Thus, two valves (for example, lockup relay valve and lockup control valve) are provided in the hydraulic controller for controlling the lockup clutch, so that if a solenoid valve driving one valve fails, a solenoid valve driving the other valve is actuated to allow the lockup clutch to release and thereby enable the vehicle to travel.
In recent years emphasis has been placed on making the automatic transmission and the hydraulic controller more compact. Consequently, a hydraulic controller having only one valve for controlling the lockup clutch (for example, only a lockup control valve) has been proposed for the purpose of conserving space in the hydraulic controller. In such a hydraulic controller, upon reaching a predetermined shifting speed (for example, a first speed stage), the lockup clutch is mechanically released and, if the solenoid valve controlling the aforementioned valve fails, the aforementioned shift stage is fixed by the failure.
In particular, an automatic transmission having a continuously variable transmission mechanism needs to detect a gear ratio for determining the aforementioned predetermined shifting speed. Accordingly, a mechanism for detecting the gear ratio is required in such an automatic transmission. Thus, although the hydraulic controller can be made more compact by employing only one valve for controlling the lockup clutch, such a mechanism for detecting gear ratio requires enlargement of the automatic transmission overall, increases the production cost, and makes the configuration more complicated.
To solve the aforementioned problems, it is an object of the present invention to provide a hydraulic controller for an automatic transmission which uses a combination of hydraulic pressures adjusted to at least three stages with a first solenoid valve and a second solenoid valve in normal operation, so that a predetermined state is established in the automatic transmission if a failure occurs in the first or second solenoid valve. Establishment of the predetermined state may be by switching pressure signal or by maintaining the pressure signals as they were immediately prior to the failure.
To achieve the aforementioned object, in one aspect the invention provides a hydraulic controller for controlling an automatic transmission by adjusting and switching hydraulic pressure from a hydraulic pressure generating source, the hydraulic controller has:
a first solenoid valve for outputting a signal pressure by adjusting a supplied hydraulic pressure;
a second solenoid valve for outputting a signal pressure by adjusting a supplied hydraulic pressure;
a first switching valve which is switched based on the signal pressure of the first solenoid valve and the signal pressure of the second solenoid valve; and
a second switching valve which is switched based on the signal pressure of the first solenoid valve and the signal pressure of the second solenoid valve,
in which at least one of the first solenoid valve and the second solenoid valve is capable of freely adjusting the signal pressure to one of three or more stages. If the first solenoid valve or the second solenoid valve becomes disabled in a predetermined state of (failure) travel, a combination of the signal pressure of the first solenoid valve and the signal pressure of the second solenoid valve, which combination is used in normal operation, for such failure so as to bring the automatic transmission into a state predetermined for such a failure.
Accordingly, at least one of the first solenoid valve and the second solenoid valve is capable of adjusting the signal pressure to one of three or more stages and the first and second switching valves are switched based on the signal pressures as adjusted by the first and second solenoid valves. Then, a combination of the signal pressures as adjusted by the first and second solenoid valves when the first and second solenoid valves are operated normally is used in order to bring the automatic transmission into a state predetermined for the event that the first or second solenoid valve becomes disabled in a given state of travel. Therefore, although necessary control of the automatic transmission is provided for normal operation, the automatic transmission can be brought into the state predetermined for the event that the first or second solenoid valve becomes disabled, i.e., cannot be operated.
In a preferred embodiment the present invention provides a hydraulic controller for an automatic transmission in which at least one of the first solenoid valve and the second solenoid valve is freely duty-controlled so that the signal pressure can be adjusted to one of three stages, namely ON control, the duty control and OFF control.
According to another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the first switching valve and the second switching valve each have a biasing member for biasing its switch position in one direction. The first switching valve receives the signal pressure of the first solenoid valve in the biasing direction of the biasing member and the signal pressure of the second solenoid valve in a direction opposite to the biasing direction of the biasing member. The second switching valve receives the signal pressure of the first solenoid valve in a direction opposite to the biasing direction of the biasing member and receives the signal pressure of the second solenoid valve in the biasing direction of the biasing member. Thus, in normal operation, the positions of the first and second switching valves can be controlled based on hydraulic pressure adjusted by the biasing force of the biasing member and that of the signal pressures of the first and second solenoid valves. If the first solenoid valve or the second solenoid valve malfunctions, the switching position of the first or second switching valve can be controlled by the adjusted pressure (signal pressure) of the other solenoid valve.
According to yet another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the first switching valve is a control valve disposed on a torque converter for switching the engagement state of the lockup clutch, and the second switching valve is a switching valve for selectively switching between at least two hydraulic pressures supplied to a hydraulic servo which engages a frictional engaging element when the vehicle travels forward or to a hydraulic servo which engages a frictional engaging element when the vehicle travels in reverse.
Thus, not only control of the automatic transmission necessary for normal operation is provided, but also in the event of failure of the first or second solenoid valve, the friction engaging element which is engaged with the lockup clutch when the vehicle travels forward or backward can be brought into a predetermined state. Further, two valves necessary for controlling the lockup clutch to a predetermined state can be reduced to only one switching valve, so that the hydraulic controller can be made more compact.
According to yet another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the predetermined state is a state in which the lockup clutch is not changed from the released state to the engaged state when the first solenoid valve and the second solenoid valve operate normally. Thus, the lockup clutch can be prevented from becoming engaged and, in particular, the engine can be kept from stopping at the same time when the vehicle stops. Consequently, even if the first and second solenoid valves malfunction, the vehicle can continue to travel.
According to a yet further preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the first solenoid valve is capable of duty-control so that the signal pressure can be selectively adjusted to three stages, i.e., ON control, the duty control and OFF control, and the second solenoid valve is capable of controlling the signal pressure to two stages, i.e., ON control and OFF control. Although the duty control can be achieved by a single solenoid valve, control of the automatic transmission necessary for normal operation is provided. If the first or second solenoid valve becomes disabled, the lockup clutch can be kept from changing from the released state to the engaged state.
Yet another preferred embodiment of the present invention provides a hydraulic controller for an automatic transmission in which, when the predetermined traveling state is that where the vehicle is stopped, a combination of signal pressure by the OFF control of the first solenoid valve and signal pressure by the ON control of the second solenoid valve is used. Thus, the stopped state of the vehicle can be controlled in normal operation and if the first or second solenoid valve becomes disabled, the lockup clutch can be kept in its released state.
According to a yet another preferred embodiment, there is provided a hydraulic controller for an automatic transmission in which when the predetermined travel state is a startup from the stopped state, a combination, for example P102, of signal pressure of the OFF control of the first solenoid valve and signal pressure of the ON control of the second solenoid valve is used. Consequently, the startup from a vehicle stop can be controlled in normal operation and if the first or second solenoid valve becomes disabled, the lockup clutch can be kept in its released state.
According to another preferred embodiment of the present invention, there is provided a hydraulic controller of an automatic transmission wherein the predetermined traveling state is a state in which the lockup clutch is released during travel and wherein a combination of the signal pressure in duty control of the first solenoid valve and the signal pressure in ON control of the second solenoid valve is used. Consequently, the released state of the lockup clutch can be controlled during normal travel and if the first or second solenoid valve becomes disabled, the lockup clutch can be kept in the released state.
According to a further preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which when the predetermined traveling state is a state in which the lockup clutch is engaged during travel, and wherein, a combination of signal pressure by the ON control of the first solenoid valve and signal pressure by the OFF control of the second solenoid valve is used. Consequently, the engagement of the lockup clutch can be controlled during normal travel.
According to a still further preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission wherein the predetermined traveling state is a state in which the lockup clutch slips, and wherein, a combination of signal pressure by the duty control of the first solenoid valve and signal pressure by the OFF control of the second solenoid valve is used. Consequently, slipping of the lockup clutch can be controlled during vehicle""s normal travel.
In a further preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the predetermined traveling state is a startup of the vehicle from a stop at a relatively low oil temperature, and wherein a combination of signal pressure by the OFF control of the first solenoid valve and signal pressure by the ON control of the second solenoid valve is used. Thus, startup from a stop can be controlled in normal operation at a relatively low oil temperature and, if the first or second solenoid valve becomes disabled, the lockup clutch can be kept in the released state.
According to a still another preferred embodiment of the present invention, there is provided a hydraulic controller of an automatic transmission in which the predetermined state of travel is a state in which the lockup clutch is released at a relatively low oil temperature, and wherein a combination of a signal pressure by the ON control of the first solenoid valve and a signal pressure by the ON control of the second solenoid valve or a combination of a signal pressure by the OFF control of the first solenoid valve and a signal pressure by the OFF control of the second solenoid valve is used in the event of the aforementioned failure, and if operation of the first solenoid valve or the second solenoid valve becomes disabled, the first solenoid valve or the second solenoid valve is turned ON or OFF so as to establish the combination. Consequently, the released state of the lockup clutch can be controlled during vehicle""s travel under normal conditions including a relatively low oil temperature and, if the first or second solenoid valve becomes disabled, the lockup clutch can be released.
According to a yet another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the first switching valve and the second switching valve each have a biasing member for biasing in a biasing direction toward one switch direction, wherein the first switching valve receives the signal pressure of the first solenoid valve in the biasing direction of the biasing member and the signal pressure of the second solenoid valve in a direction opposite to the biasing direction of the biasing member, and wherein the second switching valve receives the signal pressure of the first solenoid valve in a direction opposite to the biasing direction of the biasing member and the signal pressure of the second solenoid valve in a direction opposite to the biasing direction of the biasing member. Consequently, the positions of the first and second switching valves can be controlled based on the biasing force of the biasing member and hydraulic pressure as adjusted by the first and second solenoid valves in normal operation. If one of the first or second solenoid valves malfunctions, the switching position of the first or second switching valve can be controlled by adjusting the pressure of the other solenoid valve.
According to another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the first switching valve is a control valve disposed on a torque converter for switching the engagement state of the lockup clutch, and the second switching valve is a switching valve for selectively switching between at least two hydraulic pressures supplied to a hydraulic servo which engages a friction engaging element when the vehicle travels forward or to a hydraulic servo which engages a friction engaging element when the vehicle travels in reverse. This embodiment provides not only that control of the automatic transmission necessary in normal operation, but also if the first or second solenoid valve becomes disabled, the friction engaging element which is engaged with the lockup clutch when the vehicle travels forward or backward can be brought into the predetermined state. Further, two valves as previously necessary for controlling the lockup clutch to a predetermined state can be reduced to only one switching valve, so that the hydraulic controller can be made more compact.
According to a further preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the predetermined state is that in which the lockup clutch is not changed from the released state to the engaged state when the first solenoid valve and the second solenoid valve operate normally. Consequently, the lockup clutch can be kept from changing from the released state to the engaged state. In particular, the engine can be kept from stopping when the vehicle stops. As a result, if any trouble occurs in the first or second solenoid valves, the vehicle can continue to travel.
According to still another preferred embodiment of the present invention, there is provided a hydraulic controller for an automatic transmission in which the automatic transmission mechanism includes a continuously variable transmission mechanism. Consequently, even if control of the lockup clutch is provided for with a single switching valve, for example, need is eliminated for a mechanism for mechanically releasing the lockup clutch, responsive to detection that the continuously variable transmission mechanism is positioned to provide a predetermined shift speed. As a result, the hydraulic controller can be formed more compact thereby making the entire automatic transmission more compact, reducing production costs and simplifying the structure.